The invention relates to a data transmission device between two lines able to transmit digital data, whose logic levels correspond to an active state and an idle state of each line, by means of an interface module which provides the connection between said lines.
The invention also relates to a method of transmitting data between two lines. The device described is particularly advantageous for providing the data communication between two lines which have different reference potentials.
Such a device is described in European patent application EP 0 785 646. The device disclosed therein comprises an interface module which carries out a systematic adaptation of the logic level of the transmitted data to the characteristics of the receiving line by means of control devices and management devices which are associated with each line. The management device associated with a first line comprises means for blocking the management device associated with the second line. This blocking of the management device of the second line prevents the second line from acting as a transmitter as long as the management device associated therewith has not been unblocked by the management device of the first line. The transmitter device according to the prior art thus introduces a delay during which the line, which has just received a data, cannot in its turn send data in response.
The invention has for its object to counteract this disadvantage by proposing a data transmission device between two lines which authorizes one line, which has received a data from another line, to send back in its turn a data substantially immediately.
According to the invention, the interface module of a data transmission device as described in the opening paragraph comprises a real terminal and a virtual terminal associated with each of the lines, wherein
each real terminal is provided with means for reproducing the state of the line with which it is associated and, conversely, controlling the state of the line, and is provided with control means for controlling the state of the virtual terminal associated with the other line, and
each virtual terminal is provided with means for enabling it to enter an active state when the other line must transmit a data and to enter a passive state if this is not the case, with means for controlling the state of the associated real terminal, and with means for inhibiting the operation of the control means of the associated real terminal if and exclusively if the virtual terminal is in the active state.
The interface module of the proposed device enables to define at any given moment whether or not the associated line has a receiving character by means of the virtual terminals associated with each line. The virtual terminals enable to prevent the two lines from transmitting at the same time. The association of the virtual and real terminals associated with a first line controls the virtual terminal associated with the second line. Thus the management of the state of a virtual terminal associated with one line is carried out by the other line. A transmitting line can thus prevent the other line from transmitting data while it itself is transmitting. This blocking action is immediately interrupted the moment the transmitting line ceases to transmit data. The second line is then immediately capable of transmitting in its turn and responding. An advantage of the invention is a fast switching of the interface module which, unlike that of the device according to the prior art, does not introduce any delay between the transmission of consecutive data by each of the lines.
The invention also relates to a data transmission method between two lines able to transmit digital data, whose logic levels correspond to an active state and an idle state of said lines, by means of an interface module which provides the connection between the lines and which comprises a real terminal and a virtual terminal for each of the lines, which method comprises the following steps for the transmission of a data from a transmitting line to a receiving line:
reproduction by the real terminal associated with the transmitting line of the state of said line,
making the virtual terminal associated with the receiving line enter the active state,
controlling of the real terminal associated with the receiving line by the associated virtual terminal,
transmission of the data over the receiving line by the real terminal associated with this line.